In a general floating caliper disc brake device, a caliper arranged astride a disc rotor is supported on a mounting bracket. Further, a pair of slide pins is provided to the caliper, and fitting holes to which the pair of slide pins is slidably fitted are provided to the mounting bracket. Accordingly, the slide pins slide along the fitting holes so that the caliper is movable in a rotational axis direction of a wheel. In addition, an inner pad (friction pad) is movably supported on one side of the caliper, and an outer pad (friction pad) is fixed on the other side thereof. Moreover, a piston and a cylinder are provided to the caliper so as to press the inner pad on one side against the disc rotor (bring the inner pad into press contact with the disc rotor).
In such a floating caliper disc brake device, when a driver steps on a brake pedal, the piston supported on the cylinder advances in accordance with a leg power thus generated so that the inner pad is pressed against the disc rotor (the inner pad is brought into press contact with the disc rotor). Further, the caliper moves in the rotational axis direction of the wheel due to a reaction force generated through the advance of the piston so that the outer pad is pressed against the disc rotor (the outer pad is brought into press contact with the disc rotor). Accordingly, the inner pad and the outer pad can squeeze the disc rotor, and can therefore apply a braking force to the wheel via the disc rotor rotating integrally with the wheel.
By the way, the piston provided to the caliper is movably supported on the cylinder that is formed in the caliper, and is retained by a piston seal in a fluid tight manner. When a hydraulic fluid (brake fluid) is supplied at the time of braking to a hydraulic pressure chamber that is formed in the cylinder, the piston advances while deforming the piston seal, and when the hydraulic pressure is released (removed) from the hydraulic pressure chamber, the piston retreats toward the hydraulic pressure chamber due to a restoring force of the deformed piston seal. However, when the leg power of the driver applied to the brake pedal is excessively large, for example, along with the increase in hydraulic pressure in the hydraulic pressure chamber, the piston is pushed toward the disc rotor to a higher extent than in a predetermined setting. Hence, a relative movement occurs between the piston and the piston seal, which may hinder the piston from retreating sufficiently due to the restoring force of the piston seal. In this case, there may occur such a phenomenon that the inner pad or the outer pad is continuously held in contact with the disc rotor, that is, a so-called drag phenomenon. Further, when the drag phenomenon occurs as described above, there may occur so-called knockback, in which the inner pad or the outer pad is knocked by the rotating disc rotor and therefore the piston is pushed backward.
To address those problems, for example, a disc brake device disclosed in JP 07-253128 A, a disc brake caliper disclosed in JP 05-65929 A, a disc brake device disclosed in JP 2009-156292 A, and a floating disc brake disclosed in JP 2009-185976 A have been known conventionally.